1. Field of the Invention
This invention relates to a spray coating chamber for painting, and more particularly, it relates to a spray coating chamber free from leakage of paint mist, that is, capable of sealing therein paint mist during its painting operation. The system comprises a paint spray chamber at its middle portion between two adjacent air-curtain compartments at two opposite longitudinal sides of the chamber, wherein the contaminated air in the paint spray chamber containing floating paint mist is sucked out and the major part of such paint mist is forcibly circulated in a system of the spray coating chamber to constitute a closed circuit.
2. Description of the Prior Art
In the prior art painting chambers, there is one in which two opposite longitudinal ends are opened to constitute two openings each used for both an inlet for transferring therein works to be painted and an outlet for discharging the works painted, in which it has been inevitable that a part of the paint applied therein to the works is atomized to form a mist of air containing such atomized paint and is liable to float and circulate in the chamber, and finally it is liable to leak outside the chamber being carried by air currents in the room.
Meanwhile, it is preferred to make the particle size in the mist as small as possible in order to keep the painted film satisfactorily uniform. For this purpose of minimizing the particle size, it becomes natural to strengthen the jet force of the paint injected from the paint nozzle.
Such high speed jet of paint results in strong turbulent flow in a paint spray chamber which gives rise to undesired paint mist leakage.
In several closed loop painting systems for obviating leakage of paint mist outside, a painting chamber has been adopted, wherein only the cleaned air is circulated in the system without any leakage of harmful matter outside the system, while the air containing floating paint mist which had not been adhered to the work or works to be painted, namely, such air containing oversprayed mist is separated from such excessively sprayed paint. An example of such a system is a spray coating equipment disclosed in Japanese Utility-Model Application No. Sho 56 (1981)-26084, a prior invention by the inventor of the present invention.
The above-mentioned apparatus is constructed, in general, as shown in FIG. 1. That is, the apparatus comprises a paint spray chamber 1 located at its central portion and two static pressure compartments 2 adjacent to both axially outer sides thereof, and it further comprises a pair of air curtain compartments 3 each of which is placed adjacent to the static pressure compartment and at both axially outermost ends.
Incorporated within the paint spray chamber 1, are a paint air separator 4 for separating and catching the paint mist and a circulating fan 6 for sucking out, through a suction duct 5, the air from which the paint mist has been separated. When a part of the air in the circulating fan 6 is introduced into the static pressure compartment 2, air current flowing from the static pressure compartment 2 to the paint spray chamber 1 can be generated.
The remaining portion of the exhausted air from the circulating fan 6 is introduced to the discharge port 7 of the air curtain, while the air sucked by an air curtain suction port 8, disposed opposite to the discharge port 7, is discharged by an exhaust fan 9. By setting the amount of air sucked through the circulating fan 6 larger than that supplied from the static pressure compartments 2, a part of the discharged air from the discharge port 7 of the air curtain compartment 3 is sucked into the paint spray chamber 1 through the static pressure compartments 2. In addition, if the amount of air sucked out by the exhaust fan 9 is set larger than that of the air discharged from the air curtain discharge port 7, some amount of the air outside the system flows into the system to maintain a balance with respect to the amount. Accordingly, a major part of the air in the spray coating chamber of the equipment recirculates in the system to constitute a closed circuit and only a part of the air is expelled out being mixed with and diluted by the air outside the system.
However, in the air curtain compartment 3, discharged flow of the air curtain is liable to be increased in quantity, as it proceeds on further, by way of entrapping the air in its vicinity. Since the amount of air thus entrapped includes both the air outside the equipment and that inside, the air in the paint spray chamber 1 includes spray mist which gives rise to the flow of air curtain including mist of paint, however small in quantity the entrapped mist may be. Therefore, there has been a problem that the air curtain compartment was eventually contaminated after it was operated for a certain period of time.
There is also another type of system which is also disclosed by the present inventor and bears Japanese Utility Model Application No. 59 (1984)-04231, under the title of "A Spray Coating Chamber for Sealing Paint Mist", which improved the aforesaid apparatus of Japanese Utility Model application No. 56-26084.
The improved apparatus mentioned above has a construction substantially the same as shown in FIG. 2. That is, it also comprises a paint spray chamber placed at the center and a pair of static pressure compartments at its axially outer adjacent sides and a pair of air curtain compartments each being disposed at the adjacent outermost axial ends of the apparatus the same as shown in FIG. 1. However, the static pressure compartment 2 has been modified to further include an additional discharge port 10 so that the paint mist in the paint spray chamber cannot be entrapped into the flow of curtain air in the air curtain compartment 3.
According to the apparatus of this improved type, the flow of the air from the discharge port 10 and the flow from the discharge port 7 to the suction port 8 in the air curtain compartment 3, generally follows the path as shown in FIG. 3. However, due to the fact that there is provided only a single static pressure compartment 2 in each of the two outer parts of the paint spray chamber 1, a small amount of air mist, though it may be very little, may sometimes be entrapped into the current of curtain flow in the air curtain compartment 3. That is, the flow of air curtain from the discharge port 7 may suck out a small amount of pair mist in the paint spray chamber 1 when it proceeds while increasing the amount of air by entrapping the air in its vicinity. In such an instance, the function of the air curtain is impaired and thus results in leakage of paint mist giving rise to the contamination of the air curtain compartment. In addition, depending upon the size of the discharge port 10 in the static pressure chamber 2 and the position where it is disposed, it was found that adhering of the paint mist on the surface of surrounding walls placed at both sides and to the rearward of each discharge port was inevitable.